Cache locally whether issuers have been persisted or not already.

[phbnf]

This saves a few round trips to the IssuerStorage.

Towards #88

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 36 lines in your changes missing coverage. Please review.

Project coverage is 34.22%. Comparing base (46ec9c2) to head (d0e4643).
Report is 83 commits behind head on main.

Files	Patch %	Lines
personalities/sctfe/storage.go	0.00%	36 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #169      +/-   ##
==========================================
- Coverage   35.80%   34.22%   -1.58%     
==========================================
  Files          16       34      +18     
  Lines        1363     2992    +1629     
==========================================
+ Hits          488     1024     +536     
- Misses        801     1857    +1056     
- Partials       74      111      +37     

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